<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .left{
            width: 20%;
            height: 600px;
            background-color: beige;
            display:inline-block;
        }
        .middle{
            width: 60%;
            height: 600px;
            background-color:aqua;
            display:inline-block;
        }
        .right{
            width: 20%;
            height: 600px;
            background-color: beige;
            display:inline-block;
        }       
    </style>
</head>
<body>
    <header>header     
    </header>
    <div class="main">
        <aside class="left">left</aside><!--    
        --><section class="middle">middle</section><!--    
        --><aside class="right">right</aside>
    </div>
    <footer>footer</footer>
</body>
</html>